net/netfilter/xt_time.c

0001 /*
0002  *  xt_time
0003  *  Copyright © CC Computer Consultants GmbH, 2007
0004  *
0005  *  based on ipt_time by Fabrice MARIE <fabrice@netfilter.org>
0006  *  This is a module which is used for time matching
0007  *  It is using some modified code from dietlibc (localtime() function)
0008  *  that you can find at https://www.fefe.de/dietlibc/
0009  *  This file is distributed under the terms of the GNU General Public
0010  *  License (GPL). Copies of the GPL can be obtained from gnu.org/gpl.
0011  */
0012
0013 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0014
0015 #include <linux/ktime.h>
0016 #include <linux/module.h>
0017 #include <linux/skbuff.h>
0018 #include <linux/types.h>
0019 #include <linux/netfilter/x_tables.h>
0020 #include <linux/netfilter/xt_time.h>
0021
0022 struct xtm {
0023     u_int8_t month;    /* (1-12) */
0024     u_int8_t monthday; /* (1-31) */
0025     u_int8_t weekday;  /* (1-7) */
0026     u_int8_t hour;     /* (0-23) */
0027     u_int8_t minute;   /* (0-59) */
0028     u_int8_t second;   /* (0-59) */
0029     unsigned int dse;
0030 };
0031
0032 extern struct timezone sys_tz; /* ouch */
0033
0034 static const u_int16_t days_since_year[] = {
0035     0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334,
0036 };
0037
0038 static const u_int16_t days_since_leapyear[] = {
0039     0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335,
0040 };
0041
0042 /*
0043  * Since time progresses forward, it is best to organize this array in reverse,
0044  * to minimize lookup time.
0045  */
0046 enum {
0047     DSE_FIRST = 2039,
0048     SECONDS_PER_DAY = 86400,
0049 };
0050 static const u_int16_t days_since_epoch[] = {
0051     /* 2039 - 2030 */
0052     25202, 24837, 24472, 24106, 23741, 23376, 23011, 22645, 22280, 21915,
0053     /* 2029 - 2020 */
0054     21550, 21184, 20819, 20454, 20089, 19723, 19358, 18993, 18628, 18262,
0055     /* 2019 - 2010 */
0056     17897, 17532, 17167, 16801, 16436, 16071, 15706, 15340, 14975, 14610,
0057     /* 2009 - 2000 */
0058     14245, 13879, 13514, 13149, 12784, 12418, 12053, 11688, 11323, 10957,
0059     /* 1999 - 1990 */
0060     10592, 10227, 9862, 9496, 9131, 8766, 8401, 8035, 7670, 7305,
0061     /* 1989 - 1980 */
0062     6940, 6574, 6209, 5844, 5479, 5113, 4748, 4383, 4018, 3652,
0063     /* 1979 - 1970 */
0064     3287, 2922, 2557, 2191, 1826, 1461, 1096, 730, 365, 0,
0065 };
0066
0067 static inline bool is_leap(unsigned int y)
0068 {
0069     return y % 4 == 0 && (y % 100 != 0 || y % 400 == 0);
0070 }
0071
0072 /*
0073  * Each network packet has a (nano)seconds-since-the-epoch (SSTE) timestamp.
0074  * Since we match against days and daytime, the SSTE value needs to be
0075  * computed back into human-readable dates.
0076  *
0077  * This is done in three separate functions so that the most expensive
0078  * calculations are done last, in case a "simple match" can be found earlier.
0079  */
0080 static inline unsigned int localtime_1(struct xtm *r, time64_t time)
0081 {
0082     unsigned int v, w;
0083
0084     /* Each day has 86400s, so finding the hour/minute is actually easy. */
0085     div_u64_rem(time, SECONDS_PER_DAY, &v);
0086     r->second = v % 60;
0087     w         = v / 60;
0088     r->minute = w % 60;
0089     r->hour   = w / 60;
0090     return v;
0091 }
0092
0093 static inline void localtime_2(struct xtm *r, time64_t time)
0094 {
0095     /*
0096      * Here comes the rest (weekday, monthday). First, divide the SSTE
0097      * by seconds-per-day to get the number of _days_ since the epoch.
0098      */
0099     r->dse = div_u64(time, SECONDS_PER_DAY);
0100
0101     /*
0102      * 1970-01-01 (w=0) was a Thursday (4).
0103      * -1 and +1 map Sunday properly onto 7.
0104      */
0105     r->weekday = (4 + r->dse - 1) % 7 + 1;
0106 }
0107
0108 static void localtime_3(struct xtm *r, time64_t time)
0109 {
0110     unsigned int year, i, w = r->dse;
0111
0112     /*
0113      * In each year, a certain number of days-since-the-epoch have passed.
0114      * Find the year that is closest to said days.
0115      *
0116      * Consider, for example, w=21612 (2029-03-04). Loop will abort on
0117      * dse[i] <= w, which happens when dse[i] == 21550. This implies
0118      * year == 2009. w will then be 62.
0119      */
0120     for (i = 0, year = DSE_FIRST; days_since_epoch[i] > w;
0121         ++i, --year)
0122         /* just loop */;
0123
0124     w -= days_since_epoch[i];
0125
0126     /*
0127      * By now we have the current year, and the day of the year.
0128      * r->yearday = w;
0129      *
0130      * On to finding the month (like above). In each month, a certain
0131      * number of days-since-New Year have passed, and find the closest
0132      * one.
0133      *
0134      * Consider w=62 (in a non-leap year). Loop will abort on
0135      * dsy[i] < w, which happens when dsy[i] == 31+28 (i == 2).
0136      * Concludes i == 2, i.e. 3rd month => March.
0137      *
0138      * (A different approach to use would be to subtract a monthlength
0139      * from w repeatedly while counting.)
0140      */
0141     if (is_leap(year)) {
0142         /* use days_since_leapyear[] in a leap year */
0143         for (i = ARRAY_SIZE(days_since_leapyear) - 1;
0144             i > 0 && days_since_leapyear[i] > w; --i)
0145             /* just loop */;
0146         r->monthday = w - days_since_leapyear[i] + 1;
0147     } else {
0148         for (i = ARRAY_SIZE(days_since_year) - 1;
0149             i > 0 && days_since_year[i] > w; --i)
0150             /* just loop */;
0151         r->monthday = w - days_since_year[i] + 1;
0152     }
0153
0154     r->month    = i + 1;
0155 }
0156
0157 static bool
0158 time_mt(const struct sk_buff *skb, struct xt_action_param *par)
0159 {
0160     const struct xt_time_info *info = par->matchinfo;
0161     unsigned int packet_time;
0162     struct xtm current_time;
0163     time64_t stamp;
0164
0165     /*
0166      * We need real time here, but we can neither use skb->tstamp
0167      * nor __net_timestamp().
0168      *
0169      * skb->tstamp and skb->skb_mstamp_ns overlap, however, they
0170      * use different clock types (real vs monotonic).
0171      *
0172      * Suppose you have two rules:
0173      *  1. match before 13:00
0174      *  2. match after 13:00
0175      *
0176      * If you match against processing time (ktime_get_real_seconds) it
0177      * may happen that the same packet matches both rules if
0178      * it arrived at the right moment before 13:00, so it would be
0179      * better to check skb->tstamp and set it via __net_timestamp()
0180      * if needed.  This however breaks outgoing packets tx timestamp,
0181      * and causes them to get delayed forever by fq packet scheduler.
0182      */
0183     stamp = ktime_get_real_seconds();
0184
0185     if (info->flags & XT_TIME_LOCAL_TZ)
0186         /* Adjust for local timezone */
0187         stamp -= 60 * sys_tz.tz_minuteswest;
0188
0189     /*
0190      * xt_time will match when _all_ of the following hold:
0191      *   - 'now' is in the global time range date_start..date_end
0192      *   - 'now' is in the monthday mask
0193      *   - 'now' is in the weekday mask
0194      *   - 'now' is in the daytime range time_start..time_end
0195      * (and by default, libxt_time will set these so as to match)
0196      *
0197      * note: info->date_start/stop are unsigned 32-bit values that
0198      *   can hold values beyond y2038, but not after y2106.
0199      */
0200
0201     if (stamp < info->date_start || stamp > info->date_stop)
0202         return false;
0203
0204     packet_time = localtime_1(&current_time, stamp);
0205
0206     if (info->daytime_start < info->daytime_stop) {
0207         if (packet_time < info->daytime_start ||
0208             packet_time > info->daytime_stop)
0209             return false;
0210     } else {
0211         if (packet_time < info->daytime_start &&
0212             packet_time > info->daytime_stop)
0213             return false;
0214
0215         /** if user asked to ignore 'next day', then e.g.
0216          *  '1 PM Wed, August 1st' should be treated
0217          *  like 'Tue 1 PM July 31st'.
0218          *
0219          * This also causes
0220          * 'Monday, "23:00 to 01:00", to match for 2 hours, starting
0221          * Monday 23:00 to Tuesday 01:00.
0222          */
0223         if ((info->flags & XT_TIME_CONTIGUOUS) &&
0224              packet_time <= info->daytime_stop)
0225             stamp -= SECONDS_PER_DAY;
0226     }
0227
0228     localtime_2(&current_time, stamp);
0229
0230     if (!(info->weekdays_match & (1 << current_time.weekday)))
0231         return false;
0232
0233     /* Do not spend time computing monthday if all days match anyway */
0234     if (info->monthdays_match != XT_TIME_ALL_MONTHDAYS) {
0235         localtime_3(&current_time, stamp);
0236         if (!(info->monthdays_match & (1 << current_time.monthday)))
0237             return false;
0238     }
0239
0240     return true;
0241 }
0242
0243 static int time_mt_check(const struct xt_mtchk_param *par)
0244 {
0245     const struct xt_time_info *info = par->matchinfo;
0246
0247     if (info->daytime_start > XT_TIME_MAX_DAYTIME ||
0248         info->daytime_stop > XT_TIME_MAX_DAYTIME) {
0249         pr_info_ratelimited("invalid argument - start or stop time greater than 23:59:59\n");
0250         return -EDOM;
0251     }
0252
0253     if (info->flags & ~XT_TIME_ALL_FLAGS) {
0254         pr_info_ratelimited("unknown flags 0x%x\n",
0255                     info->flags & ~XT_TIME_ALL_FLAGS);
0256         return -EINVAL;
0257     }
0258
0259     if ((info->flags & XT_TIME_CONTIGUOUS) &&
0260          info->daytime_start < info->daytime_stop)
0261         return -EINVAL;
0262
0263     return 0;
0264 }
0265
0266 static struct xt_match xt_time_mt_reg __read_mostly = {
0267     .name       = "time",
0268     .family     = NFPROTO_UNSPEC,
0269     .match      = time_mt,
0270     .checkentry = time_mt_check,
0271     .matchsize  = sizeof(struct xt_time_info),
0272     .me         = THIS_MODULE,
0273 };
0274
0275 static int __init time_mt_init(void)
0276 {
0277     int minutes = sys_tz.tz_minuteswest;
0278
0279     if (minutes < 0) /* east of Greenwich */
0280         pr_info("kernel timezone is +%02d%02d\n",
0281             -minutes / 60, -minutes % 60);
0282     else /* west of Greenwich */
0283         pr_info("kernel timezone is -%02d%02d\n",
0284             minutes / 60, minutes % 60);
0285
0286     return xt_register_match(&xt_time_mt_reg);
0287 }
0288
0289 static void __exit time_mt_exit(void)
0290 {
0291     xt_unregister_match(&xt_time_mt_reg);
0292 }
0293
0294 module_init(time_mt_init);
0295 module_exit(time_mt_exit);
0296 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
0297 MODULE_DESCRIPTION("Xtables: time-based matching");
0298 MODULE_LICENSE("GPL");
0299 MODULE_ALIAS("ipt_time");
0300 MODULE_ALIAS("ip6t_time");